The three-dimensional X-ray crystal microscope: A new tool for materials characterization
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12/29/04
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The Three-Dimensional X-ray Crystal Microscope: A New Tool for Materials Characterization WENJUN LIU, GENE E. ICE, BENNETT C. LARSON, WENGE YANG, JONATHAN Z. TISCHLER, and JOHN D. BUDAI The three-dimensional (3-D) X-ray crystal microscope is a new nondestructive tool for the 3-D characterization of the mesoscopic and nanoscopic materials structure. A prototype microscope is installed on beamline 34-ID at the advanced photon source and has begun initial operation. The prototype microscope has a routine spatial resolution of approximately 0.5 0.5 1 m3 and can probe tens to hundreds of microns below a sample surface, depending on the composition of the sample. For each volume element measured, the microscope can determine between 10 and 16 parameters. The measured parameters are the local crystallographic phase (1 deg of freedom), the Eulerian angles of crystal orientation (3 deg of freedom), and the plastic and/or elastic strain-tensor elements (6 to 12 deg of freedom). The time required to collect each volume element varies between 1 and 14 seconds, depending on the precision of the parameters and the sample complexity. Much faster data acquisition and much better spatial resolution are certain in the near future. Some initial results are presented to illustrate how the 3-D X-ray crystal microscope can provide unprecedented information about the 3-D structure of materials.
I. INTRODUCTION
THE properties of polycrystalline materials depend on three-dimensional (3-D) scalar and tensor distributions including anisotropic/inhomogeneous elasticity, local stress, grainboundary behavior, and a host of other mesoscopic parameters. For example, macroscopic applied forces are redistributed locally by second phases, fibers, defects, grain boundaries, heterogeneous grain orientations, and plastic deformation. Unfortunately, despite remarkable recent progress in microscopy, most high-resolution microprobes are inherently surface sensitive and can only measure a 3-D structure by serial sectioning methods. Serial sectioning methods are inherently destructive, relieve local and macroscopic stress, and virtually preclude time-evolution studies. A truly nondestructive 3-D probe of crystal structure is needed to resolve long-standing fundamental issues of materials physics and to connect directly to advanced modeling efforts. To address this need, we have recently commissioned a novel 3-D X-ray crystal microscope at the advanced photon source.[1,2,3] This microscope is possible due to major technical advances in X-ray sources, detectors, and optics.[4,5] Ironically, the 3-D X-ray crystal microscope uses the oldest X-ray diffraction method: Laue diffraction. Laue diffraction is used to solve an intrinsic problem associated with conventional microdiffraction: sample rotations complicate the spatial mapping of crystalline properties below 5 m. Indeed, as described in Reference 1, diffraction with monochromatic WENJUN LIU, Unicat Beamline Scientist, is with the University of Illinois at Urbana-Champai
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